Dairy Pipeline: March 2009
Extension Dairy Veterinarian
(540) 231-5838; firstname.lastname@example.org
It is no secret that the conception rate continues to decline on dairy farms. At one time the goal for conception rate was >50%. Over time that goal fell to >40% and now herds that utilize total AI are getting 25%-35% of their cows pregnant from each service. Experts continue to argue over and work on the causes of low conception rate. Many of these problems are larger than individual dairy farms. With regards to conception rates on their farm, the most important factors dairymen can address are ensuring that the cows that are inseminated are truly in heat and the timing of breeding within the heat period.
With heat detection being such a big problem on most farms there is a tendency to call cows in heat when only the most minor of secondary signs of heat are detected. If these cows are not in heat then the chance of these cows becoming pregnant is zero. In the quest to improve heat detection make sure that you are not over zealous and call too many cows in heat that are not truly in heat.
The second factor is timing of breeding after finding cows in heat. Excellent work by Dr. Ray Nebel showed that cows are most fertile when inseminated 4-16 hours after the first standing heat. The problem when finding a cow in heat on the farm is you never know if this is the first standing heat or not. While the AM-PM rule works, when combined with the typical management systems on many farms it has the potential to result in cows being inseminated too late after their first standing heat. Take for example, a cow that is observed to be in sanding heat at 4 a.m. when cows are being gathered to be milked—this may be the first standing event for that cow or the cow may have been in heat all night. If this cow is not inseminated until after the evening milking it will be 13-23 hours after her first standing heat event. If the cow is inseminated after the morning milking then it would be 3-12 hours after the first standing event. Carefully consider how your management interacts with the timing of breeding after the cow is first detected in heat.
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